1. Field of the Invention
An exercising device which is expanded and contracted against a pneumatic resistance element.
2. Description of the Prior Art
Conventional linear exercisers employ resilient elements such as springs or elastic bands to offer resistance to manipulation. The person who is exercising typically grasps the device at its ends and pulls apart to stretch the device rectilinearly. However, this type of device has a resistance element which has several disadvantages. Elastic bands tend to deteriorate or break with age due to oxidation. Springs often are twisted out of shape or over-stretched beyond their elastic limit, or catch on fabrics and threads. Elastic bands are only capable of offering resistance in tension and consequently such elements only require exertion in stretch deformation without offering any viable resistance to compression, i.e. when tension force is terminated, compression force is not needed to return the device to it original shorter length and consequently the benefits to the user are diminished. Springs also usually are arranged only to offer resistance in tension. To have springs offer resistance in compression requires the use of compression springs which are too expensive and cumbersome for incorporation in reasonably priced exercisers.
An arm exercising device with a pneumatic resistance element is described in U.S. Pat. No. 3,471,145. Here a single knob selects alternate valves to either restrict air flow into or out of the cavity of the device, with air in the opposite sense in either case being allowed to flow freely; thus, one valve when effective allows air to flow freely out of the cavity or body of the device, e.g. when it is contracted, and controllably restricts flow of air into the cavity, i.e. when the device is expanded or lengthened, and vice versa. Thus, this patent teaches one-way pneumatic resistance, either solely in the tension mode for expansion of the device, or solely in the compression mode for contraction of the device. Said exerciser is difficult to assemble and expensive to constrict.